System for silencing radio receivers during automatic tuning thereof



Oct. 5, 1943. D. H. MITCHELL SYSTEM FOR SILENCING RADIO RECEIVERS DURING AUTOMATIC TUNING THEREOF Filed Dec. 15, 19:57

Patented Oct. 5, 1943 UNITED ,STATES y *l 2,331,999 y PATENT "OFFICE SYSTEM FonsnlENomG RADIO nncEivEns I ,DUaiNGaUToMATIo TU NiNG :rHEREoF Donald mfMitehen, omega-flu., assigner f6' Galvin Manufacturing Corporation,

Ill., a corporation of Illinois,

Application Decemner 15, 19377', sen-amo. 179,972-

This source of supplyjrnayv be used for operating electrical indicators for thegreceiven and other purposea'as well as providing silent tuning for the radioreceiver as will be more `fully described hereinafter.

Receiving sets withfautomatick tuning havernow become quite common. Someoi' ythese vsets `operate by means of a tuning' motor which, inre, .i

sponse to pressinga button or 'thejlike co rrev sponding to a particular predetenninedjstatien, is energized and will turn thegtuning condensers of the'set to the proper setting for thatstation. When the set isv thus receivingone station as de# sired,r another button maybe pressed and the motor will turn` the condensers"v togchange the tuning of the set from the one station to another station corresponding to suchjtother. button. If broadcast stations intervened between thetwo stations, -these intervening Vstation'sfwould be brought in and heard momentarily as .their frequenciesewere crossedby the tuning condensers.

Inasmuch as` normal I operatingV volume is maintained on the receiver during such tuning, suchr stations would be brought in with anobjectionable blast of sound. It is eveny worse, however, if thev set is provided with automaticl frequency control which operates independently of the tuning condensers to correct, within limita-any imperfect tuning. This automatic frequencycontrol, because of its corrective eiecttends to seize any station which isv received with suilicient strength to make such automatic frequency control effec,- tive and pullr such station into peak tuning Yas the condensers are rotated over the broadcast band. The result is that rif the desiredfpredetermined station to which the receiver is beingftuned is close to a strong station the'automatic "ire-v quency control might retain'` the wrong'station and prevent reception from the desired station.

An object of my invention lis Vto'providefina radio receiving system having? an electric` mo# tor therein, in eii'ect, a rnew source of voltage of a different value than that'suppliedto'themo' 55? Chicago" (crash-"20) 1 tor ifor operating and indicatingpurposes inthe radio vrreceiver system? l. f l 'A1-further Yobject z'of my inventiorris to provide silent accurate tuning of aJ radio receiverwhen A1 'till vfurther 'objectl of they `present`A invention isftolprevfent `alljnoise mduring tuning and simultaneously to 'prevent'theautomatic ,frequency f control from working improperly.

10 Qnefoftheffeaturesof my invention is theprovision of a tertiary'winding on a tuning lmotor fora radio receiver Ato cause the production of an induced voltage therein for ysubsequent rectifica-A tion to" be used'to/ bias the rst audio tube and 15. vstop the passage of signalstherethrough, and to be,usedtosimultaneously substantially stifle the AF.C.'z acizicrnfy y Additional objects and features will be apparentffrbm`- the following description and from the 2U drawing, in which'thejfgureis a diagrammatic illustration of the .radio` receiving 'setl chosen for illustration oi' 'this invention,V the featuresoi `the circuit towhich this `invention particularly relates `In .the form o'f the invention chosen if-or illus-1 tration the main portion of the radio, receiving set has. been'illustrated very diagrammatically,

the aerial Il through the successive stages of amplification, each of which is appropriately marked Vin the drawing. Eachy of the, various stages hasbeen shown diagrammatically asabox themixing tube or a separatetube, to produce a beat of predetermined,frequency, called theinf termediate frequencyffv These' signals of inter- 4.5 mediate frequencyare amplified twice, firstatfthe IpointgmarkedlstI. F..and then atthe point marked 2nd I. F. in the drawing. Next thev sig-f nals are rectified by the diode detector, which in.'

effect removes the intermediate frequency, leavo ing 'onlythe audio frequency;v The audiofrequency waves are amplified twice, once atthe point' marked 1st audio and'thenby the output; Thereafter, the'signals are impressed on soundwaves.

ing shown in greater detail than the 're 25 minder 0f the circuit-.

merely indicating the passage of the signal from rather than as a vtube to Aindicate the inclusion the loudspeaker i4, which converts themv into' The tube has been shown within each of the boxes labeled lst I. F. and 1st audio and the omission of conventional elements in the grid connections have been indicated by dotting these connections. The conventional connections for other tube elements have been left incomplete.

The illustrated receiving setis provided with automatic volume control, which tends to maintain a predetermined signal strength at the 2nd I. F. stage by automatically controlling the amplication of the received signals. Since the automatic volume control per se Vis not part of this invention it will be explainednonly to the extent necessary to an understanding of the present invention where it appears in the coinplete circuit combination. An 'appropriate 'connection I6 is made on the output side of the 2nd I. F. stage and is connected with a. condenser I8, which may be 150 mmf. The condenser I8 is connected to diodes 20, in the 1st audio tube 22, which have the effect of rectifyin-g the voltage transmitted through the condenser I3 kso .y that only a negative voltage is `transmitted ,through the automatic volumeI control lead 24, which extends back to the R.` F. and mixer stagesy to increasertheir negative gridv bias for the purpose of controlling `their grain and hence controlling the resulting signal strength., The effect, stated previously, is that' an undesirably high signal strength at the 2nd I. F. stage is effective through the 'automatic volume control lead 24 t0 impress a negative bias on the control grids in the earlier amplifying stages to reduce the amplification of the stages. Modulations corresponding to sound waves may be by-passed by condenser 25, one suitable value for which is .03 microfarad.

The illustrated receiving s'et is also provided withautomatic frequency control in. which a lead 26 extends from an appropriate 'connection in the diode detector stage -to a control unit |72 to alter the frequency of the oscillations enough to compensate tfor any imperfect adjustment'of the tuning condensers so as to vmake the intermediatefrequency Vthat for which the intermediate frequency stages vare designed, 'previously stated, one effect orfl'this automatic frequency co'ntrol is to cause the lset to retain a station once received, "ev'en, though thetun'ing condensers are turned slightly to the setting for a different station. In other words, as the tuning condensers arebeing turned 'to receive Aa relatively Weak station just beyond a strong station, the automatic frequency control would rtend to seize the. strong stationas it was passedand'n'ot release vit to receive the adjacent weak station.

Accordingto the present invention this" undesirable effect is prevented by 'temporarily jreducing the rsensitivity of the receiver lduring tuning 'to such anext'ent that the automatic frequency action will not beginuntil a station has actually 4been tuned in. Automatic frequency control, of course,is vdesiralrle for obtaining"peak tuning `when properly utilized. I automatic tuning, however, it is objectionable during such tuningas described above. The sig'ralstrength is reduced to prevent this effectby applying a special negative `voltage to the Iautomatic volume control lead 24, this voltage having the 'saine effect as the 'voltage normally appliedto the 'lead 24 but to a "greater'degree. The special voltage referred to is derivedfrom -a third winding-30 'on the tuning motor,-the 'third winding being in inductive relationto'the `main winding 32 and to the reverse winding i34. Whenever either of these windings are energized in response topressing a tuning button or the like for closing the supply circuit for the motor, a voltage is induced in the third Winding 30. Of course, the motor begins to operate in response to such energization immediately. The voltage provided may be in the neighborhood of 60 or 80 volts, but is alternating and must therefore be rectified. To this end the third winding 30 is connected to a condenser 36 which may be of .1 microfarad capacity, which in turn is connected by wire 3! to a plate 38 in the 1st I. F. tube 40. For convenience of distinction from the main plate 42 in this tube; this plate may be called a diode. The wire 31 is connected to condenser 44, the other side of which is connected to the other diode 46 by wire 48. The result of this connection is that when an alternating voltage is applied by the winding 3G to the condenser 35, the voltage on wire 31 is substantially rectified and another rectified voltage is impressed on wire 48. This voltage is applied bylwireh48 to the ,automatic volurne control lead 24. `The wire 48 is preferably connected between resistances 50 and 52 which comprise part of the automatic volume control system. In one form of the invention found satisfactory the resistances 50 and 52 may each be 1/4 megohm. It should also be noted thatlthe resistance 52 is connected to the power supply ofthe fset through lead 54 and to ground through .a resistance v56 which provides a proper negative grid bias. 'One value for the resistance 55 found suitable is 33 ohms.

Although the effect of applying a special negative `voltage to theautomatic volume control system, 'as 'above described, reducesu the ,signal strength suf'ciently to prevent the automatic frequency control from operating to yseize a 'f-requency being 'crossed during tuning, it `does not reduce lthe lsignal strength lsufficiently to com-r pletely eliminate sound as strong stations are crossed. "'rothis 'end an additional muting circuit is added. (The wire 31 extending between the condenser 36 and the1 diode 38 is connected by'a wirel, through resistance's 6I and G2 to the grid I(i4 of the 1st audio frequency tube 22. "I'hejfresult 'is that: when 'voltage is induced in the thirdwin'ding 30 "of the tuning motor, this voltage, rectified Vby the diodes 38 and 45, is applied 'a'sja negative grid bias to the grid 64. 'I'he constants of the set should be such 'that this bias is 'a cut-,olf bias, reducing the gain of the tube substantially to zero. With the set illustrat'ed this result was accomplished by making the 'resistances 6| and 6 2,4 respectively, .470 megol'im and-'one megohm, the condenser 65 being .l microfarad, and the resistance G1 being .22o regonm. h It should be observed `that because of the condenser '44 isolating lthe diodes 38 and l46 the voltage applied to theautornatic volume control -lead A24 and to the audio grid 64 may be independently,fcontrolledby varying the resistances asociated with each diode,'particularly the loa'drsistances 52ia`i1`d -6-1.

Itflis b'e'n very "di'clilt heretofore to completelyfsilence 'a radio receiving "set merely by automatically'operatirig 'electrical circuits. This has `been accomplished in 'the present instance by 'coinbiningtwo different routing effects to temporarily Tender Athe set substantially inoperative While such "set Vis being' tuned. `First is the -muting effect of the negative voltage impressed on -the automatic volume control lead 24, which greatly reduces `the signal Strength reaching the ist I. Vl?. -stage of amplification.

' ing? *means- L and effective fatli't'he preliminary stagesof'amplicationg and" anotherxfmuting means connected with the rectifying means'and *effective inan. audiostage Vof: amplificationffor The secondi mutingleffect isy the 'application f Ia cut-off bia-s to the grid E4`of the 1st.au'dio`fre quency:v tube. 22,`which should cut the-gain to zeroat this point. This combinationofth'e"two muting effects controlled "jointly, simultanecusly and automatically Yby the' third winding" 30'2w`hen the tuningmotoris operated; willrender thereceiving set completely 'silent even .thoughfitlwas formerly operatingzwith high volumeoutput;`4

It is thus seen v'from Vthev above =`descriptio`n that I'provide avery simple and! inexpensive means in a radioreceiverisystememploying-an electric motor for supplying vltage'toilthe receiver system different in value than that for the source of 4supplyto such motor." The transformer action with the third winding may be suitably employed to provide a larger or smaller voltage than that for the motor, and as previously mentioned, this may be used for the purpose of lighting a tuning indicating lamp, for instance, for other types of operating indication in the receiver system, as well as for silent tuning as above more particularly described. The constants, such as resistance or condenser values which have been given heretofore, are merely illustrative. Widely different values may be found entirely satisfactory and with different receiving sets will probably be necessary. These values are given as examples of values which have been found satisfactory in commercial embodiments of the invention.

The'disclosures of this application are illus trative and the invention is not to be limited by them. In fact, if modifications or improvements are not at once obvious, they may be devised in the courseof time to make additional use of the broad ideas taught and covered by this application. I

I claim:

1. A radio receiver system including in combination, a radio receiver and an electric motor for directly driving tuning means for said radio receiver, said driving motor including a main field winding, a reversing field winding and a tertiary Winding in inductive relation with said main field and reversing windings, a sourcel of voltage for said motor, with said tertiary winding in said driving motor acting to provide an alternating voltage output therefrom, means in said radio receiver for rectifying said voltage output from said tertiary winding, and means for utilizing said rectified voltage for silencing said radio receiver during the tuning operation of said driving motor.

2. A system for rendering a radio receiver circuit having an audio tube and an automatic volume control network substantially inoperative during the tuning thereof by an electric motor, including in combination means for developing an induced voltage at said motor upon energization of said motor, means for rectifying said voltage, means for utilizing a portion of said rectified voltage to bias said audio tube and reduce its gain, and means for applying another portion of said rectified voltage to the automatic volume control network of said receiver to reduce the sensitivity of said receiver.

3. A radio receiving set provided with a tuning motor, characterized by the provision `of means for silencing the setl during operation of the tuning motor, said means comprising a third winding in inductive relationship with the motor to be energized when the motor is energized, rectifying means connected with the third winding, muting means connected with Athe rectifyfurther mutingfthe" set.` n t 4*."A'radio` receivingfset having'an automatic volume control circuit; ani-f automatic yfrequency control circuit; and'v a tuning motor, characterized bythe provision ofathird' winding fortlietuning motor in inductive relation? thereto whereby voltage is induced in fthe" third winding whenthe motor' is energized,v meansj-forrectifying `the voltage, meansV `for- `applying Jthe! rectifled'fvoltageto the automatic volume control 'circuit forreduc'- ing the signal strength at vthe point where `.the signalsN govern the automatic frequency control sufficiently to render the automatic frequency control'` circuit ineffective to seize a frequency be-i V ing crossed in tuning, 'and means for applying the rectified "voltage as a cut-offbias on the grid of an audio frequency amplifying tube.

5. Arradio receiving set having an automatic` Afrequency ,control circuit. and a tuning motor,

characterized 'by the provision of a third winding for the tuning motor inindu'ctive relation thereto whereby voltage is induced in thethirdwinding when the 'motor is energized, means for rectifying the voltage, and means for applying the s rectified-voltage to a grid of an amplifying tube in advance of the automatic frequency control circuit for reducing the signal strength at the point where the signals govern the automatic frequency control sufficiently to render the automatic frequency control circuit ineffective to seize a frequency being crossed in tuning.

6. A radio receiving set having an automatic volume control circuit, an automatic frequency control circuit, and a tuning motor, characterized by the provision of a third winding for the tuning motor in inductive relation thereto whereby voltage is induced therein when the motor is energized, means for rectifying` the voltage, and means for applying the rectified voltage to the automatic volume control circuit for reducing the signalv strength sufliciently to render the automatic frequency control circuit ineffective to seize a frequency being crossed in tuning.

7. A radio` receiving set having an automatic volume control circuit, an automatic frequency control circuit, and a tuning motor, characterized by the provision ofa third winding for the tuning motor in inductive relation thereto whereby voltage is induced therein when the motor is energized, means for rectifying the voltage, means for applying the rectified voltage to the' automatic volume control circuit for reducing the signal strength sufficiently to render the automatic frequency control circuit ineffective to seize a frequency being crossed in tuning, and Ameans for applying the rectified voltage as a cut-off bias on the grid of an audio frequency amplifying tube, the rectifying means comprising a pair of diodes Within a vacuum tube, electrically separated by a condenser, whereby the rectified voltage produced with the aid of each diode may be independently predetermined, one diode being connected to the automatic volume control circuit and the other to the audio grid.

8. A radio receiving set including an amplifyl on the motor for producing an alternating voltage during operation of the motor, rectifying means forrectifying the voltage, and means for .applying the rectified voltage to said grid -as a gain reducing bias.

;9. vRadio apparatus including a lradio receiver circuit having tuning means and including an audio tube therein having agrid, a driving motor for operating the vtuning means'fvor isaid 1radio receiver circuit, said motor having 'means including an independent .energizing winding fthereon for supplying -an alternating voltage t0 Salaireceiver Acircuit during .operation of the motor, means for rectifying said alternating voltagafand means for applying -the -rectied Ivoltage to the grid of said audio tube t0 lbias .said tube and render .the lsame inoperativeior am-plifying'a sig- 15 nal therethrough during, operation of said driving motor. t

10. Radio ,apparatus having movable means and including Aa plurality of tubes in electrical connection in said apparatus, -a rotary driving motor operatively connected .to said movable means to drive the same and rincluding ,a field winding, said motor having .another winding thereon in inductive relation to said vfield Winding for producing lan operating voltage `during rotation of said motor in driving `said movable means, and means coupling at least one of said tubes with said other winding.

DONALD H. sMITCHELL. 

